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Ocean salinity is derived mainly from the weathering of rocks and the transport of dissolved salts from the land, with lesser contributions from hydrothermal vents in the seafloor. Evaporation of ocean water and formation of sea ice further increase the salinity of the ocean. However these processes which increase salinity are continually counterbalanced by processes that decrease salinity, such as the continuous input of fresh water from rivers, precipitation of rain and snow, and the melting of ice. The two most prevalent ions in seawater are chloride and sodium. Together, they make up around 85 per cent of all dissolved ions in the ocean. Magnesium and sulfate ions make up most of the rest. Salinity varies with temperature, evaporation, and precipitation. It is generally low at the equator and poles, and high at mid-latitudes. | 9 | Geochemistry |
Two main trends impinge on the industry. On the supply side, biotechnology is rapidly gaining importance. In the synthesis of small molecule fine chemicals, the use of biocatalysts and microbial fermentation enable both a more sustainable and economic production than conventional organic chemistry. In the synthesis of big molecules, such as biopharmaceuticals, it is the method of choice. Biopharmaceuticals are expected to grow 15% per year, three times as fast as small molecule drugs. Five of the top ten drugs were biopharmaceuticals in 2010 (see table 6), and this is expected to grow to eight by 2016 (see table 2).
On the demand side, the main customer base for fine chemicals, the pharmaceutical industry, is faced with slower growth of demand, patent expirations of many lucrative blockbuster drugs and stalling new product launches. In order to restrain these challenges, the leading companies are implementing restructuring programs. They comprise a reduction of in-house chemical manufacturing and plant eliminations. Outsourcing is moving up from a purely opportunistic to a strategic approach. It is difficult to make a judgment, whether the positive or negative effects of these initiatives will prevail. In a worst-case scenario, a condition could develop, whereby even top-tier mid-sized, family-owned fine-chemical companies with state-of-the-art plants and processes could be relegated to producing small quantities of fine chemicals for new life-science products in late stage of development. In agro fine chemicals, the active ingredients become more sophisticated and performing. Therefore, they require multipurpose instead of dedicated plants prevailing in the industry so far. At the same token, outsourcing is gaining ground.
Globalization results in a shift of fine chemical production from the industrialized to developing countries. The latter benefit not only from a "low cost / high skill" advantage, but also from a rapidly rising domestic demand for Western medicine. Despite the mantras of Western industry leaders, the cost advantage of the Asian producers is going to persist. As the pharmemerging countries mainly use generics, their market share continues to grow to the detriment of originator pharmaceuticals and agrochemicals. This is also the case for biosimilars, the generic versions of biopharmaceuticals.
As a consequence of the harsh business climate, many Western fine chemical companies or divisions created during the "irrational exuberance" at the end of the 20th century already have exited from the sector. Others will follow suit or will be acquired by private equity firms. Survival strategies include implementation of lean production principles originally developed by the automotive industry and extending the business model to include also contract research at the beginning and active drug formulation towards the end of the added value chain. This latter strategy, however, is not finding unanimous approval by industry experts.
Although the demand for fine chemicals on the merchant market has not grown to the extent originally anticipated, fine chemicals still provide attractive opportunities for well-run companies, which are fostering the critical success factors, namely running fine chemicals as a core business, pursuing niche technologies—primarily biotechnology—and taking advantage of the opportunities offered by the Asian market. | 0 | Organic Chemistry |
AMP deaminase deficiency (formally known as myoadenylate deaminase deficiency or MADD) is a metabolic myopathy which results in excessive AMP buildup brought on by exercise. AMP deaminase is needed to convert AMP into IMP in the purine nucleotide cycle. Without this enzyme, the excessive AMP buildup is initially due to the adenylate kinase (myokinase) reaction which occurs after a muscle contraction. However, AMP is also used to allosterically regulate the enzyme myophosphorylase (see Glycogen phosphorylase § Regulation), so the initial buildup of AMP triggers the enzyme myophosphorylase to release muscle glycogen into glucose-1-P (glycogen→glucose-1-P), which eventually depletes the muscle glycogen, which in turn triggers protein metabolism, which then produces even more AMP. In AMP deaminase deficiency, excess adenosine is converted into uric acid in the following reaction:
:AMP → Adenosine → Inosine → Hypoxanthine → Xanthine → Uric Acid | 1 | Biochemistry |
Polymerization of epoxides gives polyethers. For example ethylene oxide polymerizes to give polyethylene glycol, also known as polyethylene oxide. The reaction of an alcohol or a phenol with ethylene oxide, ethoxylation, is widely used to produce surfactants:
:ROH + n CHO → R(OCH)OH
With anhydrides, epoxides give polyesters. | 0 | Organic Chemistry |
To make a geometrically stable structure in a mineral, atoms must fit together in terms of both their size and charge. The atoms have to fit together so that their electron shells can interact with one another and they also have to produce a neutral molecule. For these reasons the sizes and electron shell structure of atoms determine what element combinations are possible and the geometrical form that various minerals take. Because electrons are donated and received, it is the ionic radius of the element that controls the size and determines how atoms fit together in minerals. | 3 | Analytical Chemistry |
The mole (symbol mol) is a unit of measurement, the base unit in the International System of Units (SI) for amount of substance, a quantity proportional to the number of elementary entities of a substance. One mole contains exactly elementary entities (approximately 602 sextillion or 602 billion times a trillion), which can be atoms, molecules, ions, or other particles. The number of particles in a mole is the Avogadro number (symbol N) and the numerical value of the Avogadro constant (symbol N) expressed in mol. The value was chosen based on the historical definition of the mole as the amount of substance that corresponds to the number of atoms in 12 grams of C, which made the mass of a mole of a compound expressed in grams numerically equal to the average molecular mass of the compound expressed in daltons. With the 2019 redefinition of the SI base units, the numerical equivalence is now only approximate but may be assumed for all practical purposes.
The mole is widely used in chemistry as a convenient way to express amounts of reactants and amounts of products of chemical reactions. For example, the chemical equation can be interpreted to mean that for each 2 mol molecular hydrogen (H) and 1 mol molecular oxygen (O) that react, 2 mol of water (HO) form. The concentration of a solution is commonly expressed by its molar concentration, defined as the amount of dissolved substance per unit volume of solution, for which the unit typically used is mole per litre (mol/L). | 3 | Analytical Chemistry |
The application of DC electric fields is known to reduce the flow stress of metals and metal alloys while increasing the fracture strain. Several mechanisms have been put forth to explain this effect including Joule heating, electron wind force, dissolution of metallic bonds, and unpinning of dislocations due the induction of magnetic fields. None of these mechanisms on their own can sufficiently explain the full extent of electroplasticity in metals. The application of electric fields has been shown to enhance the effect of superplasticity which occurs in polycrystalline metals at high homologous temperatures (T>0.5Tm). This is likely due to the electric field reducing cavitation, which can lead to premature fracture, and grain growth, which can prevent superplastic flow due to grain boundary sliding, in addition to reducing the activation energy for grain boundary sliding. The strength of the electroplastic effect scales with the magnitude of the applied electric field past some threshold value. While the application of an electric field typically augments the plasticity of metals there are alloy systems that show a reduction in plasticity. Conrad and Li found that the activation energy for grain boundary sliding in Zn-5 wt.% Al increased by nearly 20% under the application of a 2 DC electric field, resulting in more difficult deformation. | 7 | Physical Chemistry |
The Martin Medal is an award given for outstanding contributions to the advancement of separation science. The award is presented by The Chromatographic Society, a UK-based organization promoting all aspects of chromatography and related separation techniques. The award is named after Professor Archer J.P Martin, who contributed to the invention of partition chromatography, and shared the 1952 Nobel Prize in Chemistry. | 3 | Analytical Chemistry |
Combustion spraying guns use oxygen and fuel gases. The fuel gases are potentially explosive. In particular, acetylene may only be used under approved conditions. Oxygen, while not explosive, will sustain combustion and many materials will spontaneously ignite if excessive oxygen levels are present. Care must be taken to avoid leakage and to isolate oxygen and fuel gas supplies when not in use. | 8 | Metallurgy |
The best method of controlling hydrogen damage is to control contact between the metal and hydrogen. Many steps can be taken to reduce the entry of hydrogen into metals during critical operations like melting; casting; working (rolling, forging, etc.); welding; and surface preparation, like chemical cleaning, electroplating, and corrosion during their service life. Control of the environment and metallurgical control of the material to decrease its susceptibility to hydrogen are the two major approaches to reduce hydrogen damage. | 8 | Metallurgy |
Margules expressed the intensive excess Gibbs free energy of a binary liquid mixture as a power series of the mole fractions x:
In here the A, B are constants, which are derived from regressing experimental phase equilibria data.
Frequently the B and higher order parameters are set to zero. The leading term assures that the excess Gibbs energy becomes zero at x=0 and x=1. | 7 | Physical Chemistry |
DSIF plays the same role for HIV-1 gene expression as it would normally in transcription. This is because P-TEFb phosphorylates DSIF the same regardless of whether or not P-TEFb goes through normal cellular regulation or bypasses it due to Tat. | 1 | Biochemistry |
Cycle of quantification/qualification (C) is a parameter used in real-time polymerase chain reaction techniques, indicating the cycle number where a PCR amplification curve meets a predefined mathematical criterion. A C may be used for quantification of the target sequence or to determine whether the target sequence is present or not.
Two criteria to determine the C are used by different thermocyclers:
threshold cycle (C) is the number of cycles required for the fluorescent signal to cross a given value threshold. Usually, the threshold is set above the baseline, about 10 times the standard deviation of the noise of the baseline, to avoid random effects on the C. However, the threshold shouldn't be set much higher than that to avoid reduced reproducibility due to uncontrolled factors.
Crossing point (Cp) and Take off point (TOP) are the cycle value of the maximum second derivative of the amplification curve. | 1 | Biochemistry |
Copper can exist in non-ionic form (as Cu) or in one of two redox states: Cu (reduced) or Cu (oxidized). Each form of Cu has a specific distribution of electrons (i.e., electron configuration), tabulated below:
The electronic configurations of Cu control the number and types of bonds Cu can form with other atoms (e.g., see Copper Biology section). These diverse coordination chemistries are what enable Cu to participate in many different biological and chemical reactions.
Finally, due to its full d-orbital, Cu has diamagnetic resonance. In contrast, Cu has one unpaired electron in its d-orbital, giving it paramagnetic resonance. The different resonances of the Cu ions enable determination of Cu's redox state by techniques such as electron paramagnetic resonance (epr) spectroscopy, which can identify atoms with unpaired electrons by exciting electron spins. | 9 | Geochemistry |
In many cases, gatekeeper genes encode a system of checks and balances that monitor cell division and death. When tissue damage occurs, for example, products of gatekeeper genes ensure that balance of cell growth over cellular death remains in check. In the presence of competent gatekeeper genes, mutations of other genes do not lead to on-going growth imbalances.
Mutations altering these genes lead to irregular growth regulation and differentiation. Each cell type has only one, or at least only very few, gatekeeper genes. If a person is predisposed to cancer, they have inherited a mutation in one of two copies of a gatekeeper gene. Mutation of the alternate allele leads to progression to neoplasia.
Historically, the term gatekeeper gene was first coined in association with the APC gene, a tumor suppressor that is consistently found to be mutated in colorectal tumors. Gatekeeper genes are in fact specific to the tissues in which they reside.
The probability that mutations occur in other genes increases when DNA repair pathway mechanisms are damaged as a result of mutations in caretaker genes. Thus, the probability that a mutation will take place in a gatekeeper gene increases when the caretaker gene has been mutated.
Apoptosis, or induced cell suicide, usually serves as a mechanism to prevent excessive cellular growth. Gatekeeper genes regulate apoptosis. However, in instances where tissue growth or regrowth is warranted, these signals must be inactivated or net tissue regeneration would be impossible. Thus, mutations in growth-controlling genes would lead to the characteristics of uncontrolled cellular proliferation, neoplasia, while in a parallel cell that had no mutations in the gatekeeper function, simple cell death would ensue. | 1 | Biochemistry |
It was given a Royal Charter in 1975. In 1977 it became the sixteenth constituent of the •Council of Engineering Institutions, which became the Engineering Council in 1981. | 8 | Metallurgy |
Alpha-substitution reactions occur at the position next to the carbonyl group,
the α-position, and involve the substitution of an α hydrogen atom
by an electrophile, E, through either an enol or enolate ion intermediate. | 0 | Organic Chemistry |
The term is often used without a definition. Some authors define the term "high-energy" to be equivalent to "chemically unstable", while others reserve the term for high-energy phosphates, such as the Great Soviet Encyclopedia which defines the term "high-energy compounds" to refer exclusively to those.
The IUPAC glossary of terms used in ecotoxicology defines a primary producer as an "organism capable of using the energy derived from light or a chemical substance in order to manufacture energy-rich organic compounds". However, IUPAC does not formally define the meaning of "energy-rich". | 1 | Biochemistry |
A diverse and large pool of synthetic molecules have been reported to act as ion transporters in lipid membranes. A selection is described here to demonstrate the breadth of feasible structures and attainable functions. Comprehensive reviews for the literature up to 2010 are available in a tripartite series. | 6 | Supramolecular Chemistry |
The solvothermal approach is the most common used in the literature but typically requires long reaction times due to the insolubility of the organic SBUs in nonorganic media and the time necessary to reach thermodynamic COF products. | 6 | Supramolecular Chemistry |
* Infant formula: Historically HMOs were not part of infant formula, and bottle-fed babies could not benefit from their positive health effects. However recently more and more HMOs, including 2'-Fucosyllactose and Lacto-N-neotetraose, are being added as supplements to modern infant formula. Recently an infant formula with a combination of 5 different HMOs (2′-fucosyllactose, 2′,3-di-fucosyllactose, lacto-N-tetraose, 3′-sialyllactose, and 6′-sialyllactose) was tested in a clinical trial with positive effects on gut microflora. However it is important to note that even this type of infant formula is far from the natural abundance of nearly 200 HMOs present in human milk.
* Irritable bowel syndrome: Human milk oligosaccharides are also used to treat the symptoms of irritable bowel syndrome (IBS), which is a gastrointestinal disorder affecting 10–15% of the developed world. A 12-week treatment with an orally taken HMO mixture showed significant improvement of the life quality of IBS patients. | 0 | Organic Chemistry |
Nickel-based superalloys are used in load-bearing structures requiring the highest homologous temperature of any common alloy system (Tm = 0.9, or 90% of their melting point). Among the most demanding applications for a structural material are those in the hot sections of turbine engines (e.g. turbine blade). They comprise over 50% of the weight of advanced aircraft engines. The widespread use of superalloys in turbine engines coupled with the fact that the thermodynamic efficiency of turbine engines is a function of increasing turbine inlet temperatures has provided part of the motivation for increasing the maximum-use temperature of superalloys. From 1990-2020, turbine airfoil temperature capability increased on average by about 2.2 °C/year. Two major factors have made this increase possible:
* Processing techniques that improved alloy cleanliness (thus improving reliability) and/or enabled the production of tailored microstructures such as directionally solidified or single-crystal material.
* Alloy development resulting in higher temperature materials primarily through the additions of refractory elements such as Re, W, Ta, and Mo.
About 60% of the temperature increases related to advanced cooling, while 40% have resulted from material improvements. State-of-the-art turbine blade surface temperatures approach 1,150 C. The most severe stress and temperature combinations correspond to an average bulk metal temperature approaching 1,000 C..
Although Ni-based superalloys retain significant strength to 980 C, they tend to be susceptible to environmental attack because of the presence of reactive alloying elements. Surface attack includes oxidation, hot corrosion, and thermal fatigue. | 8 | Metallurgy |
Bioaerosols are typically introduced into the air via wind turbulence over a surface. Once airborne they typically remain in the planetary boundary layer (PBL), but in some cases reach the upper troposphere and stratosphere. Once in the atmosphere, they can be transported locally or globally: common wind patterns/strengths are responsible for local dispersal, while tropical storms and dust plumes can move bioaerosols between continents. Over ocean surfaces, bioaerosols are generated via sea spray and bubbles. | 7 | Physical Chemistry |
The study of network motifs was pioneered by Holland and Leinhardt who introduced the concept of a triad census of networks. They introduced methods to enumerate various types of subgraph configurations, and test whether the subgraph counts are statistically different from those expected in random networks.
This idea was further generalized in 2002 by Uri Alon and his group when network motifs were discovered in the gene regulation (transcription) network of the bacteria E. coli and then in a large set of natural networks. Since then, a considerable number of studies have been conducted on the subject. Some of these studies focus on the biological applications, while others focus on the computational theory of network motifs.
The biological studies endeavor to interpret the motifs detected for biological networks. For example, in work following, the network motifs found in E. coli were discovered in the transcription networks of other bacteria as well as yeast and higher organisms. A distinct set of network motifs were identified in other types of biological networks such as neuronal networks and protein interaction networks.
The computational research has focused on improving existing motif detection tools to assist the biological investigations and allow larger networks to be analyzed. Several different algorithms have been provided so far, which are elaborated in the next section in chronological order.
Most recently, the acc-MOTIF tool to detect network motifs was released. | 1 | Biochemistry |
An early application of a DNA database was the compilation of a Mitochondrial DNA Concordance, prepared by Kevin W. P. Miller and John L. Dawson at the University of Cambridge from 1996 to 1999 from data collected as part of Millers PhD thesis. There are now several DNA databases in existence around the world. Some are private, but most of the largest databases are government-controlled. The United States maintains the largest DNA database, with the Combined DNA Index System (CODIS) holding over 13 million records as of May 2018. The United Kingdom maintains the National DNA Database (NDNAD), which is of similar size, despite the UKs smaller population. The size of this database, and its rate of growth, are giving concern to civil liberties groups in the UK, where police have wide-ranging powers to take samples and retain them even in the event of acquittal. The Conservative–Liberal Democrat coalition partially addressed these concerns with part 1 of the Protection of Freedoms Act 2012, under which DNA samples must be deleted if suspects are acquitted or not charged, except in relation to certain (mostly serious or sexual) offenses. Public discourse around the introduction of advanced forensic techniques (such as genetic genealogy using public genealogy databases and DNA phenotyping approaches) has been limited, disjointed, unfocused, and raises issues of privacy and consent that may warrant the establishment of additional legal protections.
The U.S. Patriot Act of the United States provides a means for the U.S. government to get DNA samples from suspected terrorists. DNA information from crimes is collected and deposited into the CODIS database, which is maintained by the FBI. CODIS enables law enforcement officials to test DNA samples from crimes for matches within the database, providing a means of finding specific biological profiles associated with collected DNA evidence.
When a match is made from a national DNA databank to link a crime scene to an offender having provided a DNA sample to a database, that link is often referred to as a cold hit. A cold hit is of value in referring the police agency to a specific suspect but is of less evidential value than a DNA match made from outside the DNA Databank.
FBI agents cannot legally store DNA of a person not convicted of a crime. DNA collected from a suspect not later convicted must be disposed of and not entered into the database. In 1998, a man residing in the UK was arrested on accusation of burglary. His DNA was taken and tested, and he was later released. Nine months later, this man's DNA was accidentally and illegally entered in the DNA database. New DNA is automatically compared to the DNA found at cold cases and, in this case, this man was found to be a match to DNA found at a rape and assault case one year earlier. The government then prosecuted him for these crimes. During the trial the DNA match was requested to be removed from the evidence because it had been illegally entered into the database. The request was carried out.
The DNA of the perpetrator, collected from victims of rape, can be stored for years until a match is found. In 2014, to address this problem, Congress extended a bill that helps states deal with "a backlog" of evidence.
PIDS(Plant international DNA-fingerprinting system) is an open source web server and free software based plant international DNA fingerprinting system.
It manages huge amount of microsatellite DNA fingerprint data, performs genetic studies, and automates collection, storage and maintenance while decreasing human error and increasing efficiency.
The system may be tailored to specific laboratory needs, making it a valuable tool for plant breeders, forensic science, and human fingerprint recognition.
It keeps track of experiments, standardizes data and promotes inter-database communication.
It also helps with the regulation of variety quality, the preservation of variety rights and the use of molecular markers in breeding by providing location statistics, merging, comparison and genetic analysis function. | 1 | Biochemistry |
Glucuronidation is often involved in drug metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids. These linkages involve glycosidic bonds. | 0 | Organic Chemistry |
Apart from the original evidence provided by Männig and Nöth, the total synthesis of (+)-ptilocaulin also demonstrates selective hydroboration of a terminal alkene in the presence of a ketone.
In terms of regioselectivity, the catalyzed hydroboration differs from the uncatalyzed parallel. Depending on the ligands and the alkene, either Markovnikov or anti-Markovnikov product result. The difference in regioselectivity is more pronounced in the hydroboration of vinylarenes with HBcat. Wilkinson's catalyst or the cation Rh(COD) (in the presence of PPh) produces the Markovnikov product. The anti-Markovnikov product is produced in the absence of a catalyst. It is worth noticing that the use of RhCl·nH2O produces selectively the anti-Markovnikov product. To account for the high regioselectivity of catalyzed hydroboration, Hayashi proposed a mechanism involving a η-benzylrhodium complex.
Catalyzed hydroboration-oxidation of substituted alkenes can be rendered enantioselective. In 1990, Brown and co-workers achieved asymmetric hydroboration using an achiral catalyst and chiral borane sources derived from ephedrine and pseudoephedrine. In most cases, the regioselectivity was poor although the ee values can be close to 90%.
Use of a chiral catalyst and an achiral borane source is more common, e.g. chiral diphosphines such as BINAP.
Styrene or its simple derivatives are usually the prochiral substrate.
Enantioselectivity tends to be lowered with ortho-substituents on the aromatic ring, as well as further substitution on the olefin. Successful results have also been obtained on other reactants. The second class of ligands is phosphinamine ligands. In 1993, Brown first reported the successful use of QUINAP in asymmetric alkene hydroboration. QUINAP improve upon the intolerance of substitution on the aromatic ring as observed for diphosphine ligands. Reactions using styrene and derivatives with electron-donating groups on the para position still gave high ee values. Similar results were also obtained on cyclic vinyl arenes. Such results expand the scope of asymmetric hydroboration to more sterically demanding alkenes. Several new ligands of this class have also been developed. Some recent results are summarized below.
The studies above have all utilized oxidation of the boronate esters to produce alcohols, which is a severe limitation to the synthetic scope of such species, especially when they can be made enantioselectively. Another important class of compounds that can be derived from boronate esters is α-substituted benzylamines, some of which are commercially useful. The synthesis of such chiral amines via catalytic hydroboration involves conversion of the catecholboronate ester to trialkylborane by diethyl zinc or methylmagnesium chloride. Reaction of the trialkylborane with hydroxylamine-O-sulfonic acid produces primary benzylamines. Secondary amines can also be prepared by in situ formation of N-chloramines. | 0 | Organic Chemistry |
ortho-Carborane is the organoboron compound with the formula CBH. The prefix ortho is derived from ortho. It is the most prominent carborane. This derivative has been considered for a wide range of applications from heat-resistant polymers to medical applications. It is a colorless solid that melts, without decomposition, at 320 °C | 7 | Physical Chemistry |
In a chain-growth polymerization reaction, the reactive end-groups of a polymer chain react in each propagation step with a new monomer molecule transferring the reactive group to the last unit. Here the chain carrier is the polymer molecule with a reactive end-group, and at each step it is regenerated with the addition of one monomer unit: | 7 | Physical Chemistry |
Neurturin signaling is mediated by the activation of a multi-component receptor system including the ret tyrosine kinase (RET), a cell-surface bound GDNF family receptor-α (GFRα) protein, and a glycosyl phosphatidylinositol (GPI)-linked protein. Neurturin preferentially binds to the GFRα2 co-receptor. Upon assembly of the complex, specific tyrosine residues are phosphorylated within two molecules of RET that are brought together to initiate signal transduction and the MAP kinase signaling pathway. | 1 | Biochemistry |
By analogy to the above, one can use an anion exchange (positively charged) column surface chemistry to reduce the influence on retention of cationic (positively charged) functional groups for a set of analytes, such as when selectively isolating phosphorylated peptides or sulfated polysaccharide molecules. Use of a pH between 1 and 2 pH units will reduce the polarity of two of the three ionizable oxygens of the phosphate group, and thus will allow easy desorption from the (oppositely charged) surface chemistry. It will also reduce the influence of negatively charged carboxyls in the analytes, since they will be protonated at this low a pH value, and thus contribute less overall polarity to the molecule. Any common, positively charged amino groups will be repelled from the column surface chemistry and thus these conditions enhance the role of the phosphate's polarity (as well as other neutral polar groups) in the separation. | 1 | Biochemistry |
There are many design criteria which vary according to the type of disc and the required filtering capacity. The typical filter for extracting iron contains 12 ceramic filtering plates of the filtering elements (discs), which have a diameter of about 2705 mm, making the total filter surface 120 m. This filter is most suited to filter feed slurries with high solid concentrations (5-20% w/w) and particles ranging in size from 1–700 µm. The area of the filters available in the ceramic filter is up to 45 m, making them useful for metal and mineral concentrate processing.
The ceramic discs are available in two types, cast plate and membrane plate. The cast plate is a one piece ceramic plate with a homogeneous surface and a granulated core. The filter medium of the cast plate is the thick walls, separated by ceramic granules. These features form a rigid mechanical structure. The membrane plate type contains a thin membrane over a coarser core and a multi-layer porous structure made of aluminium oxide. The coarse part of the equipment provides mechanical strength to its structure while the intermediate layer acts as a membrane carrier. The outer layer membrane acts as a filtering layer. The filtration layer of the ceramic filter has uniform pores, which means that only a certain size of particles can be filtered by using vacuum ceramic filters. | 3 | Analytical Chemistry |
Some members of this class of drugs inhibit the synthesis of cell walls in susceptible microbes by inhibiting peptidoglycan synthesis. The core class (including vancomycin) binds to acyl--alanyl--alanine in lipid II, preventing the addition of new units to the peptidoglycan. Of this core class, one may distinguish multiple generations: the first generation includes vancomycin and teicoplanin, while the semisynthetic second generation includes lipoglycopeptides like telavancin, oritavancin and dalbavancin. The extra lipophilicity not only enhances Lipid II binding, but also creates a second mechanism of action whereby the antibiotic dissolves into the membrane and makes it more permeable.
Corbomycin and complestatin are structurally and ancestrally related to vancomycin, but they work by inhibiting autolysins through binding to peptidoglycan, therefore preventing cell division, neither is an approved drug.
Ramoplanin, although a "glycopeptide" in the literal sense, has a quite different structural core. It not only binds to Lipid II, but also attacks MurG and transglycosylases (glycosyltransferases) which polymerize amino acid/sugar building blocks into peptidoglycan. It has been described as a "first-in-class" antibiotic, representing glycolipodepsipeptide antibiotics.
Bleomycin also has a different core. Its mode of action is also unrelated to the cell wall, instead causing DNA damage in tumor cells. | 0 | Organic Chemistry |
The Irving Langmuir Prize in Chemical Physics is awarded annually, in even years by the American Chemical Society and in odd years by the American Physical Society. The award is meant to recognize and encourage outstanding interdisciplinary research in chemistry and physics, in the spirit of Irving Langmuir. A nominee must have made an outstanding contribution to chemical physics or physical chemistry within the 10 years preceding the year in which the award is made. The award will be granted without restriction, except that the recipient must be a resident of the United States.
The award was established in 1931 by Dr. A.C. Langmuir, brother of Nobel Prize-winning chemist Irving Langmuir, to recognize the best young chemist in the United States. A $10,000 prize was to be awarded annually by the American Chemical Society. The first recipient was Linus Pauling. In 1964, the General Electric Foundation took over the financial backing of the prize, which was renamed the Irving Langmuir Award and the modern selection process was created. In 2006 the GE Global Research took over sponsorship of the award, and since 2009 the award has been co-sponsored between GE Global Research and the ACS Division of Physical Chemistry. | 7 | Physical Chemistry |
Oligosaccharides have diverse structures. The number of monosaccharides, ring size, the different anomeric stereochemistry, and the existence of the branched-chain sugars all contribute to the amazing complexity of the oligosaccharide structures. The essence of the reducing oligosaccharide synthesis is connecting the anomeric hydroxyl of the glycosyl donors to the alcoholic hydroxyl groups of the glycosyl acceptors. Protection of the hydroxyl groups of the acceptor with the target alcoholic hydroxyl group unprotected can assure regiochemical control. Additionally, factors such as the different protecting groups, the solvent, and the glycosylation methods can influence the anomeric configurations. This concept is illustrated by an oligosaccharide synthesis in Scheme 1. Oligosaccharide synthesis normally consists of four parts: preparation of the glycosyl donors, preparation of the glycosyl acceptors with a single unprotected hydroxyl group, the coupling of them, and the deprotection process. | 0 | Organic Chemistry |
The exact purity of very fine precious metals such as platinum, gold and silver can be of great interest. Based on the system of millesimal fineness, a metal is said to be one nine or one nine fine if it is 900 fine, or 90% pure. A metal that is 990 fine is then described as two nines fine and one that is 999 fine is described as three nines fine. Thus, nines are a logarithmic scale of purity for very fine precious metals. Similarly, percentages ending in a 5 have conventional names, traditionally the number of nines, then "five", so 999.5 fine (99.95% pure) is "three nines five", abbreviated 3N5.
Canada's Big Maple Leaf, a coin made of gold at 5N (99.999%) purity, stands as the purest gold coin ever minted, anywhere. The purest gold ever achieved was reportedly produced at the Perth Mint in 1957, at "almost six nines" (99.9999%) purity, as measured by the Worshipful Company of Goldsmiths of London. | 8 | Metallurgy |
Sterimol parameters are built upon the Corey-Pauling-Koltun atomic models, which take into consideration the Van der Waals radii of each atom in the molecule. Unlike most other steric parameters such as A-value, Taft parameters and Tolman cone angle, which group all the spatial information into a single cumulative value, Sterimol parameters consist of three sub-parameters: one length parameter (L), and two width parameters (B, B). The three parameters add together to profile the 3-dimentional spatial information of a molecule.
In order to define the Sterimol parameters of a molecule, an axis needs to be defined at first. Since Sterimol parameters are usually applied for describing the bulkiness of a certain substituent which is attached to the substrate, the default choice of the axis is the one that passes through the atoms which link the substrate and substituent together. This axis is defined as the X-axis.
Once the X-axis has been defined, the Sterimol parameters can be assigned. Take the 1,2-dimethylpropyl group as an example (Figure 1). The length parameter (L) refers to the farthest extension of the substituents in the direction parallel to the X axis (shown in Figure 1, left). The width parameters can be assigned from the point of view which is perpendicular to the X axis. The width parameter B refers to the minimal profile width of the substituents on the linking atom from the X axis, while parameter B refers to the maximal width from the same axis (shown in Figure 1, right).
Sterimol B–B parameters were initially used for obtaining the maximal width. However, in his second generation Sterimol approach, Verloop pointed out that due to their directional dependence on Sterimol B, discrepancies arose when computing those three parameters in cases where B can point to multiple directions. Since Sterimol B and B hardly contributed significantly to any regression functions obtained, and Sterimol B was practically equal to B, the parameters B–B were omitted.
Sterimol B parameter demonstrates the steric effects imposed by branching at the linking atom of a substituent. The more branches the linking atom bears, the larger Sterimol B value the substituent has. On the other hand, Sterimol B parameter is more susceptible to the steric effects of the substituent's terminus. In general, Sterimol B represents vicinal steric effects of the substituent, while Sterimol B represents remote steric effects.
Several open-source programs have already included the feature of calculating Sterimol parameters, such as Morfeus, Kallisto, and dbstep. | 4 | Stereochemistry |
Tribocorrosion is a material degradation process due to the combined effect of corrosion and wear. The name tribocorrosion expresses the underlying disciplines of tribology and corrosion. Tribology is concerned with the study of friction, lubrication and wear (its name comes from the Greek "tribo" meaning to rub) and corrosion is concerned with the chemical and electrochemical interactions between a material, normally a metal, and its environment. As a field of research tribocorrosion is relatively new, but tribocorrosion phenomena have been around ever since machines and installations are being used.
Wear is a mechanical material degradation process occurring on rubbing or impacting surfaces, while corrosion involves chemical or electrochemical reactions of the material. Corrosion may accelerate wear and wear may accelerate corrosion. One then speaks of corrosion accelerated wear or wear accelerated corrosion. Both these phenomena, as well as fretting corrosion (which results from small amplitude oscillations between contacting surfaces) fall into the broader category of tribocorrosion. Erosion-corrosion is another tribocorrosion phenomenon involving mechanical and chemical effects: impacting particles or fluids erode a solid surface by abrasion, chipping or fatigue while simultaneously the surface corrodes. | 8 | Metallurgy |
In organic chemistry and organometallic chemistry, carbon–hydrogen bond activation ( activation) is a type of organic reaction in which a carbon–hydrogen bond is cleaved and replaced with a bond (X ≠ H is typically a main group element, like carbon, oxygen, or nitrogen). Some authors further restrict the term C–H activation to reactions in which a C–H bond, one that is typically considered to be "unreactive", interacts with a transition metal center M, resulting in its cleavage and the generation of an organometallic species with an M–C bond. The intermediate of this step (sometimes known as the activation step) could then undergo subsequent reactions with other reagents, either in situ or in a separate step, to produce the functionalized product.
The alternative term functionalization is used to describe any reaction that converts a relatively inert bond into a bond, irrespective of the reaction mechanism (or with an agnostic attitude towards it). In particular, this definition does not require the cleaved C–H bond to initially interact with the transition metal in the reaction mechanism. This broader definition encompasses all reactions that would fall under the restricted definition of C–H activation given above. However, it also includes iron-catalyzed alkane C–H hydroxylation reactions that proceed through the oxygen rebound mechanism (e.g. cytochrome P450 enzymes and their synthetic analogues), in which a metal–carbon bond is not believed to be involved. Likewise, the ligand-based reactivity of many metal carbene species with hydrocarbons in which the carbene carbon inserts into a C–H bond, again without interaction of the hydrocarbon C–H bond with the metal, also falls under this category. Often, when authors make the distinction between C–H functionalization and activation, they will restrict the latter to the narrow sense. | 0 | Organic Chemistry |
Paralogs: FAM227A
Orthologs: FAM227B is present in Deuterostomia and Protostomia, dating as far back as porifera. FAM227B is not present in choanoflagellates, and gene alignment sequences have shown that FAM227B is a rapidly evolving gene due to its evolution trajectory compared to cytochrome c and fibrinogen alpha. | 1 | Biochemistry |
* Ascorbic acid is easily oxidized and so is used as a reductant in photographic developer solutions (among others) and as a preservative.
* In fluorescence microscopy and related fluorescence-based techniques, ascorbic acid can be used as an antioxidant to increase fluorescent signal and chemically retard dye photobleaching.
* It is also commonly used to remove dissolved metal stains, such as iron, from fiberglass swimming pool surfaces.
* In plastic manufacturing, ascorbic acid can be used to assemble molecular chains more quickly and with less waste than traditional synthesis methods.
* Heroin users are known to use ascorbic acid as a means to convert heroin base to a water-soluble salt so that it can be injected.
* As justified by its reaction with iodine, it is used to negate the effects of iodine tablets in water purification. It reacts with the sterilized water, removing the taste, color, and smell of the iodine. This is why it is often sold as a second set of tablets in most sporting goods stores as Potable Aqua-Neutralizing Tablets, along with the potassium iodide tablets.
*Intravenous high-dose ascorbate is being used as a chemotherapeutic and biological response modifying agent. It is undergoing clinical trials.
* It is sometimes used as a urinary acidifier to enhance the antiseptic effect of methenamine. | 1 | Biochemistry |
Endoglin has been found to be an auxiliary receptor for the TGF-beta receptor complex. It thus is involved in modulating a response to the binding of TGF-beta1, TGF-beta3, activin-A, BMP-2, BMP-7 and BMP-9. Beside TGF-beta signaling endoglin may have other functions. It has been postulated that endoglin is involved in the cytoskeletal organization affecting cell morphology and migration.
Endoglin has a role in the development of the cardiovascular system and in vascular remodeling. Its expression is regulated during heart development . Experimental mice without the endoglin gene die due to cardiovascular abnormalities. | 1 | Biochemistry |
An inherent limitation to the immunogold technique is that the gold particle is around 15-30 nm away from the site to which the primary antibody is bound (when using a primary and secondary antibodies labeling strategy). The precise location of the targeted molecule can therefore not be accurately calculated. Gold particles can be created with a diameter of 1 nm (or lower) but another limitation is then realized—at these sizes the gold label becomes hard to distinguish from tissue structure.
Thin sections are required for immunogold labeling and these can produce misleading images; a thin slice of a cell component may not give an accurate view of its three-dimensional structure. For example, a microtubule may appear as a spike depending on which plane the sectioning occurred. To overcome this limitation serial sections can be taken, which can then be compiled into a three-dimensional image.
A further limitation is that antibodies and gold particles cannot penetrate the resin used to embed samples for imaging. Thus, only accessible molecules can be targeted and visualized. Labeling prior to embedding the sample can reduce the negative impact of this limitation. | 1 | Biochemistry |
* Positions of the CBED disks are the same as the positions of the Bragg peaks and are given approximately by the relation:
where is the distance between the crystallographic planes , is the Bragg angle, is an integer, and is the wavelength of the probing electrons.
* The beam convergence semi-angle - is controlled by the C2 aperture. The probing beam convergence semi-angle, , is of the order of milliradians, ranging from 0.1˚ to 1˚. For small convergence semi-angle, the CBED disks do not overlap with each other, whereas for larger semi-convergence angles, the disks overlap.
* The diameter of a CBED disk is given by the beam convergence semi-angle :
* Defocus : The distance between the crossover of the probing beam and the position of the specimen is called the defocus distance . The sample can be moved along the axis. At a defocus distance, both the direct space and reciprocal space information are visible in the CBED pattern. | 3 | Analytical Chemistry |
Poly(phthalaldehyde) was first reported in 1967 by Chuji Aso and Sanae Tagami from the department of Organic Synthesis at Kyushu University by an addition homopolymerization reaction of aromatic o-phthalaldehyde. This polymer, consisting of a polyacetal main chain, is still to date, the only aromatic aldehyde that can be homopolymerized through a chain-growth polymerization method. It is a white brittle solid with a low ceiling temperature and significant self-immolative properties. It has gathered significant attention in recent years especially in the development of novel responsive materials and applications. | 7 | Physical Chemistry |
*1972–1975 – Associate Member, Viking Lander Science Team, NASA
*1979–1982 – – Member, Committee on Response Strategies to Unusual Chemical Hazards, Assembly of Life Sciences, National Research Council
*1982 – U.S. Coordinator, U.S.-Japan Joint Seminar on “Microcolumn Separation Methods and their Ancillary Techniques,” Honolulu, Hawaii
*1980–1984 – Member, Advisory Committee to the Analytical Chemistry Division, Oak Ridge National Laboratory
*1986 – Instructor, ACS Short Course on Supercritical Fluid Chromatography
*1988, 1990 – Organizing Committee, International Symposium, “Microcolumn Separation Methods,” Bloomington, IN and Aronberg, Sweden
*1988, 1991 – Scientific Committee, International Symposium, “HPLC 88” and “HPLC 92”
*1977–Pres. – Instructor, ACS Short Course on Capillary Gas Chromatography
*1978–Pres. – ACS Lecture Tour Speaker
*1990–Pres. – Scientific Committee, International Symposia on Capillary Chromatography
*1994 – Scientific Committee, Glycobiology: Analytical Methods
*2003 – Member of the Center for the Integrative Study of Animal Behavior, Indiana University
*2004 – Member of the Indiana University Cancer Center, IU School of Medicine | 3 | Analytical Chemistry |
Mechanical revolving blade fans are made in a wide range of designs. They are used on the floor, table, desk, or hung from the ceiling (ceiling fan), and can be built into a window, wall, roof, etc. Electronic systems generating significant heat such as computers incorporate fans. Appliances such as hair dryers and space heaters also use fans. They move air in air-conditioning systems and in automotive engines. Fans used for comfort inside a room create a wind chill by increasing the heat transfer coefficient but do not lower temperatures directly. Fans used to cool electrical equipment or in engines or other machines do cool the equipment directly by exhausting hot air into the cooler environment outside of the machine so that cooler air flows in.
There are three main types of fans used for moving air, axial, centrifugal (also called radial) and cross flow (also called tangential). The American Society of Mechanical Engineers Performance Testing Code 11 (PTC) provides standard procedures for conducting and reporting tests on fans, including those of the centrifugal, axial, and mixed flows. | 7 | Physical Chemistry |
A monosaccharide often switches from the acyclic (open-chain) form to a cyclic form, through a nucleophilic addition reaction between the carbonyl group and one of the hydroxyl groups of the same molecule. The reaction creates a ring of carbon atoms closed by one bridging oxygen atom. The resulting molecule has a hemiacetal or hemiketal group, depending on whether the linear form was an aldose or a ketose. The reaction is easily reversed, yielding the original open-chain form.
In these cyclic forms, the ring usually has five or six atoms. These forms are called furanoses and pyranoses, respectively—by analogy with furan and pyran, the simplest compounds with the same carbon-oxygen ring (although they lack the double bonds of these two molecules). For example, the aldohexose glucose may form a hemiacetal linkage between the aldehyde group on carbon 1 and the hydroxyl on carbon 4, yielding a molecule with a 5-membered ring, called glucofuranose. The same reaction can take place between carbons 1 and 5 to form a molecule with a ring, called glucopyranose. Cyclic forms with a seven-atom ring (the same of oxepane), rarely encountered, are called heptoses.
For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three.
Cyclization creates a new stereogenic center at the carbonyl-bearing carbon. The −OH group that replaces the carbonyls oxygen may end up in two distinct positions relative to the rings midplane. Thus each open-chain monosaccharide yields two cyclic isomers (anomers), denoted by the prefixes α- and β-. The molecule can change between these two forms by a process called mutarotation, that consists in a reversal of the ring-forming reaction followed by another ring formation. | 0 | Organic Chemistry |
Previous reports have identified as many as eight splice variants, which are translated into seven isoforms of the protein. Apoptosis-inducing Fas receptor is dubbed isoform 1 and is a type 1 transmembrane protein. Many of the other isoforms are rare haplotypes that are usually associated with a state of disease. However, two isoforms, the apoptosis-inducing membrane-bound form and the soluble form, are normal products whose production via alternative splicing is regulated by the cytotoxic RNA binding protein TIA1.
The mature Fas protein has 319 amino acids, has a predicted molecular weight of 48 kilodaltons and is divided into three domains: an extracellular domain, a transmembrane domain, and a cytoplasmic domain. The extracellular domain has 157 amino acids and is rich in cysteine residues. The transmembrane and cytoplasmic domains have 17 and 145 amino acids respectively. Exons 1 through 5 encode the extracellular region. Exon 6 encodes the transmembrane region. Exons 7-9 encode the intracellular region. | 1 | Biochemistry |
Sample preparation of the OPV is of the utmost importance when performing pc-AFM studies. The sampling substrate is recommended to be conductive, as well as transparent, to the light source which is irradiated upon it. Numerous studies have used ITO-coated glass as their conductive substrate. Because of high cost of ITO, however, there have been attempts to utilize other semiconducting layers, such as zinc oxide (ZnO) and carbon nanotubes as an alternative to ITO. Although these semiconductors are relatively inexpensive, high quality ITO layers are still being used extensively for PV applications. Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), more commonly known as PEDOT:PSS, is a transparent, polymeric conductive layer which is usually placed between the ITO and the active OPV layer. The PEDOT:PSS is a conductive polymer is stable over various applied charges. In most studies, PEDOT:PSS is spin-coated onto the ITO-coated glass substrates directly after plasma cleaning of the ITO. Plasma cleaning, as well as halo-acid etching, have been shown to improve the surface uniformity and conductivity of the substrate. This PEDOT:PSS layer is then annealed to the ITO prior to spin-coating the OPV layer onto the substrate. Studies by Pingree et al. have shown the direct correlation between annealing time and both peak and average photocurrent generation. Once this OPV film is spin-coated onto the substrate, it is then annealed at temperatures between 70 and 170 °C, for periods up to an hour depending on the procedure as well as OPV being used. | 6 | Supramolecular Chemistry |
Most photoluminescent events, in which a chemical substrate absorbs and then re-emits a photon of light, are fast, in the order of 10 nanoseconds. Light is absorbed and emitted at these fast time scales in cases where the energy of the photons involved matches the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the electron which absorbed the photon (energy) undergoes an unusual intersystem crossing into an energy state of different (usually higher) spin multiplicity (see term symbol), usually a triplet state. As a result, the excited electron can become trapped in the triplet state with only "forbidden" transitions available to return to the lower energy singlet state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. Most phosphorescent compounds are still relatively fast emitters, with triplet decay-times in the order of milliseconds.
Common examples include the phosphor coatings used in fluorescent lamps, where phosphorescence on the order of milliseconds or longer is useful for filling in the "off-time" between AC current cycles, helping to reduce "flicker". Phosphors with faster decay times are used in applications like the pixels excited by free electrons (cathodoluminescence) in cathode-ray tube television-sets, which are slow enough to allow the formation of a picture as the electron beam scans the screen, but fast enough to prevent the frames from blurring together. Even substances commonly associated with fluorescence may in fact be prone to phosphorescence, such as the liquid dyes found in highlighter pens, which is a common problem in liquid dye lasers. The onset of phosphorescence in this case can sometimes be reduced or delayed significantly by the use of triplet-quenching agents. | 7 | Physical Chemistry |
In organisms, methylglyoxal is formed as a side-product of several metabolic pathways. Methylglyoxal mainly arises as side products of glycolysis involving glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. It is also thought to arise via the degradation of acetone and threonine. Illustrative of the myriad pathways to MGO, aristolochic acid caused 12-fold increase of methylglyoxal from 18 to 231 μg/mg of kidney protein in poisoned mice. It may form from 3-aminoacetone, which is an intermediate of threonine catabolism, as well as through lipid peroxidation. However, the most important source is glycolysis. Here, methylglyoxal arises from nonenzymatic phosphate elimination from glyceraldehyde phosphate and dihydroxyacetone phosphate (DHAP), two intermediates of glycolysis. This conversion is the basis of a potential biotechnological route to the commodity chemical 1,2-propanediol.
Since methylglyoxal is highly cytotoxic, several detoxification mechanisms have evolved. One of these is the glyoxalase system. Methylglyoxal is detoxified by glutathione. Glutathione reacts with methylglyoxal to give a hemithioacetal, which converted into S--lactoyl-glutathione by glyoxalase I. This thioester is hydrolyzed to -lactate by glyoxalase II. | 1 | Biochemistry |
Flucloxacillin, also known as floxacillin, is an antibiotic used to treat skin infections, external ear infections, infections of leg ulcers, diabetic foot infections, and infection of bone. It may be used together with other medications to treat pneumonia, and endocarditis. It may also be used prior to surgery to prevent Staphylococcus infections. It is not effective against methicillin-resistant Staphylococcus aureus (MRSA). It is taken by mouth or given by injection into a vein or muscle.
Common side effects include an upset stomach. Other side effects may include muscle or joint pains, shortness of breath, and liver problems. It appears to be safe during pregnancy and breastfeeding. It should not be used in those who are allergic to penicillin. It is a narrow-spectrum beta-lactam antibiotic of the penicillin class. It is similar in effect to cloxacillin and dicloxacillin, being active against penicillinase forming bacteria.
Flucloxacillin was patented in 1961. It is not commonly used in the United States or Canada as of 2011. | 4 | Stereochemistry |
Absorption bands in the radio frequency range are found in NMR spectroscopy. The frequency ranges and intensities are determined by the magnetic moment of the nuclei that are observed, the applied magnetic field and temperature occupation number differences of the magnetic states. | 7 | Physical Chemistry |
The transmission of protons through a sample can also be used to get information about the sample.
Channeling is one of the processes that can be used to study crystals. | 7 | Physical Chemistry |
Sepro-Sizetec Screens are used for a variety of particle size separation and dewatering duties in mineral processing and aggregate applications. In mineral processing applications, particle size separation is of utmost importance in order to optimize crushing, grinding and gravity separation as well as many other processes. In aggregate applications, proper size separation and dewatering is essential to generate a saleable product. High capacity capable and featuring interchangeable screen decks, Sepro-Sizetec Screens are used for gold ore processing, fine aggregates, industrial minerals, soil remediation and coal processing applications. | 8 | Metallurgy |
Researchers began questioning the nature of "tail states" in disordered semiconductors in the 1950s. It was found that such tails arise from the strains sufficient to push local states past the band edges.
In 1953, the Austrian-American physicist Franz Urbach (1902–1969) found that such tails decay exponentially into the gap. Later, photoemission experiments delivered absorption models revealing temperature dependence of the tail.
A variety of amorphous crystalline solids expose exponential band edges via optical absorption. The universality of this feature suggested a common cause. Several attempts were made to explain the phenomenon, but these could not connect specific topological units to the electronic structure. | 3 | Analytical Chemistry |
Lectin is a kind of protein that can bind to carbohydrate with their carbohydrate recognition domains (CRDs). We could use different CRD to classify them. | 0 | Organic Chemistry |
Electron backscatter diffraction (EBSD) is a scanning electron microscopy (SEM) technique used to study the crystallographic structure of materials. EBSD is carried out in a scanning electron microscope equipped with an EBSD detector comprising at least a phosphorescent screen, a compact lens and a low-light camera. In the microscope an incident beam of electrons hits a tilted sample. As backscattered electrons leave the sample, they interact with the atoms and are both elastically diffracted and lose energy, leaving the sample at various scattering angles before reaching the phosphor screen forming Kikuchi patterns (EBSPs). The EBSD spatial resolution depends on many factors, including the nature of the material under study and the sample preparation. They can be indexed to provide information about the material's grain structure, grain orientation, and phase at the micro-scale. EBSD is used for impurities and defect studies, plastic deformation, and statistical analysis for average misorientation, grain size, and crystallographic texture. EBSD can also be combined with energy-dispersive X-ray spectroscopy (EDS), cathodoluminescence (CL), and wavelength-dispersive X-ray spectroscopy (WDS) for advanced phase identification and materials discovery.
The change and sharpness of the electron backscatter patterns (EBSPs) provide information about lattice distortion in the diffracting volume. Pattern sharpness can be used to assess the level of plasticity. Changes in the EBSP zone axis position can be used to measure the residual stress and small lattice rotations. EBSD can also provide information about the density of geometrically necessary dislocations (GNDs). However, the lattice distortion is measured relative to a reference pattern (EBSP). The choice of reference pattern affects the measurement precision; e.g., a reference pattern deformed in tension will directly reduce the tensile strain magnitude derived from a high-resolution map while indirectly influencing the magnitude of other components and the spatial distribution of strain. Furthermore, the choice of EBSP slightly affects the GND density distribution and magnitude. | 7 | Physical Chemistry |
The parameters of the Rosin–Rammler distribution can be determined by refactoring the distribution function to the form
Hence the slope of the line in a plot of
: versus
yields the parameter and is determined by substitution into | 7 | Physical Chemistry |
Spontaneous deamination is the hydrolysis reaction of cytosine into uracil, releasing ammonia in the process. This can occur in vitro through the use of bisulfite, which deaminates cytosine, but not 5-methylcytosine. This property has allowed researchers to sequence methylated DNA to distinguish non-methylated cytosine (shown up as uracil) and methylated cytosine (unaltered).
In DNA, this spontaneous deamination is corrected for by the removal of uracil (product of cytosine deamination and not part of DNA) by uracil-DNA glycosylase, generating an abasic (AP) site. The resulting abasic site is then recognised by enzymes (AP endonucleases) that break a phosphodiester bond in the DNA, permitting the repair of the resulting lesion by replacement with another cytosine. A DNA polymerase may perform this replacement via nick translation, a terminal excision reaction by its 5⟶3 exonuclease activity, followed by a fill-in reaction by its polymerase activity. DNA ligase then forms a phosphodiester bond to seal the resulting nicked duplex product, which now includes a new, correct cytosine (Base excision repair). | 1 | Biochemistry |
All redox reactions take place in the hydrophilic domain of complex I. NADH initially binds to complex I, and transfers two electrons to the flavin mononucleotide (FMN) prosthetic group of the enzyme, creating FMNH. The electron acceptor – the isoalloxazine ring – of FMN is identical to that of FAD. The electrons are then transferred through the FMN via a series of iron-sulfur (Fe-S) clusters, and finally to coenzyme Q10 (ubiquinone). This electron flow changes the redox state of the protein, inducing conformational changes of the protein which alters the pK values of ionizable side chain, and causes four hydrogen ions to be pumped out of the mitochondrial matrix. Ubiquinone (CoQ) accepts two electrons to be reduced to ubiquinol (CoQH). | 1 | Biochemistry |
Hydrion is a trademarked name for a popular line of compound pH indicators, marketed by Micro Essential Laboratory Inc., exhibiting a series of color changes (typically producing a recognizably different color for each pH unit) over a range of pH values. Although solutions are available, the most common forms of Hydrion are a series of papers impregnated with various mixtures of indicator dyes. It is considered a "universal indicator". | 3 | Analytical Chemistry |
Iminium ions are potent electrophiles useful for generating C-C bonds in complex molecules. However, the condensation of amines with carbonyl compounds to form iminium ions is often unfavorable, sometimes requiring harsh dehydrating conditions. Thus, alternative methods for iminium ion generation, particularly by oxidation from the corresponding amine, are a valuable synthesis tool. Iminium ions can be generated from activated amines using Ir(dtbbpy)(ppy)PF as a photoredox catalyst. This transformation is proposed to occur by oxidation of the amine to the aminium radical cation by the excited photocatalyst. This is followed by hydrogen atom transfer to a superstoichimetric oxidant, such as trichloromethyl radical (CCl to form the iminium ion). The iminium ion is then quenched by reaction with a nucleophile. Related transformations of amines with a wide variety of other nucleophiles have been investigated, such as cyanide (Strecker reaction), silyl enol ethers (Mannich reaction), dialkylphosphates, allyl silanes (aza-Sakurai reaction), indoles (Friedel-Crafts reaction), and copper acetylides.
Similar photoredox generation of iminium ions has furthermore been achieved using purely organic photoredox catalysts, such as Rose Bengal and Eosin Y.
An asymmetric variant of this reaction utilizes acyl nucleophile equivalents generated by N-heterocyclic carbene catalysis. This reaction method sidesteps the problem of poor enantioinduction from chiral photoredox catalysts by moving the source of enantioselectivity to the N-heterocyclic carbene. | 5 | Photochemistry |
Almost all proteins that are destined to the secretory pathway have a sequence consisting of 5-30 hydrophobic amino acids on the N-terminus, which is commonly referred to as the signal peptide, signal sequence or leader peptide. Signal peptides form alpha-helical structures. Proteins that contain such signals are destined for either extra-cellular secretion, the plasma membrane, the lumen or membrane of either the (ER), Golgi or endosomes. Certain membrane-bound proteins are targeted to the secretory pathway by their first transmembrane domain, which resembles a typical signal peptide.
In prokaryotes, signal peptides direct the newly synthesized protein to the SecYEG protein-conducting channel, which is present in the plasma membrane. A homologous system exists in eukaryotes, where the signal peptide directs the newly synthesized protein to the Sec61 channel, which shares structural and sequence similarity with SecYEG, but is present in the endoplasmic reticulum. Both the SecYEG and Sec61 channels are commonly referred to as the translocon, and transit through this channel is known as translocation. While secreted proteins are threaded through the channel, transmembrane domains may diffuse across a lateral gate in the translocon to partition into the surrounding membrane. | 1 | Biochemistry |
Ankyrin repeat and kinase domain containing 1 (ANKK1) also known as protein kinase PKK2 or sugen kinase 288 (SgK288) is an enzyme that in humans is encoded by the ANKK1 gene. The ANKK1 is a member of an extensive family of the Ser/Thr protein kinase family, and protein kinase superfamily involved in signal transduction pathways. | 1 | Biochemistry |
The main tools are proton and carbon-13 NMR spectroscopy, IR Spectroscopy, Mass spectrometry, UV/Vis Spectroscopy and X-ray crystallography. | 0 | Organic Chemistry |
Angiogenin is a key protein implicated in angiogenesis in normal and tumor growth. Angiogenin interacts with endothelial and smooth muscle cells resulting in cell migration, invasion, proliferation and formation of tubular structures. Ang binds to actin of both smooth muscle and endothelial cells to form complexes that activate proteolytic cascades which upregulate the production of proteases and plasmin that degrade the laminin and fibronectin layers of the basement membrane. Degradation of the basement membrane and extracellular matrix allows the endothelial cells to penetrate and migrate into the perivascular tissue. Signal transduction pathways activated by Ang interactions at the cellular membrane of endothelial cells produce extracellular signal-related kinase1/2 (ERK1/2) and protein kinase B/Akt. Activation of these proteins leads to invasion of the basement membrane and cell proliferation associated with further angiogenesis. The most important step in the angiogenesis process is the translocation of Ang to the cell nucleus. Once Ang has been translocated to the nucleus, it enhances rRNA transcription by binding to the CT-rich (CTCTCTCTCTCTCTCTCCCTC) angiogenin binding element (ABE) within the upstream intergenic region of rDNA, which subsequently activates other angiogenic factors that induce angiogenesis.
However, angiogenin is unique among the many proteins that are involved in angiogenesis in that it is also an enzyme with an amino acid sequence 33% identical to that of bovine pancreatic ribonuclease (RNase A). Ang has the same general catalytic properties as RNase A, it cleaves preferentially on the 3' side of pyrimidines and follows a transphosphorylation/hydrolysis mechanism. Although angiogenin contains many of the same catalytic residues as RNase A, it cleaves standard RNA substrates 10–10 times less efficiently than RNase A. The reason for this inefficiency is due to the 117 residue consisting of a glutamine, which blocks the catalytic site. Removal of this residue through mutation increases the ribonuclease activity between 11 and 30 fold. Despite this apparent weakness, the enzymatic activity of Ang appears to be essential for biological activity: replacements of important catalytic site residues (histidine-13 and histidine-114) invariably diminish both the ribonuclease activity toward tRNA by 10,000 fold and almost abolishes angiogenesis activities completely. | 1 | Biochemistry |
Anion-exchange chromatography is a process that separates substances based on their charges using an ion-exchange resin containing positively charged groups, such as diethyl-aminoethyl groups (DEAE). In solution, the resin is coated with positively charged counter-ions (cations). Anion exchange resins will bind to negatively charged molecules, displacing the counter-ion. Anion exchange chromatography is commonly used to purify proteins, amino acids, sugars/carbohydrates and other acidic substances with a negative charge at higher pH levels. The tightness of the binding between the substance and the resin is based on the strength of the negative charge of the substance. | 3 | Analytical Chemistry |
Gold nanoshells, coated silica nanoparticles with a thin layer of gold. have been conjugated to antibodies (anti-HER2 or anti-IgG) via PEG linkers. After incubation of SKBr3 cancer cells with the gold nanoshells, an 820 nm laser was used to irradiate the cells. Only the cells incubated with the gold nanoshells conjugated with the specific antibody (anti-HER2) were damaged by the laser. Another category of gold nanoshells are gold layer on liposomes, as soft template. In this case, drug can also be encapsulated inside and/or in bilayer and the release can be triggered by laser light. | 5 | Photochemistry |
Exome sequencing is especially effective in the study of rare Mendelian diseases, because it is an efficient way to identify the genetic variants in all of an individual's genes. These diseases are most often caused by very rare genetic variants that are only present in a tiny number of individuals; by contrast, techniques such as SNP arrays can only detect shared genetic variants that are common to many individuals in the wider population. Furthermore, because severe disease-causing variants are much more likely (but by no means exclusively) to be in the protein coding sequence, focusing on this 1% costs far less than whole genome sequencing but still detects a high yield of relevant variants.
In the past, clinical genetic tests were chosen based on the clinical presentation of the patient (i.e. focused on one gene or a small number known to be associated with a particular syndrome), or surveyed only certain types of variation (e.g. comparative genomic hybridization) but provided definitive genetic diagnoses in fewer than half of all patients. Exome sequencing is now increasingly used to complement these other tests: both to find mutations in genes already known to cause disease as well as to identify novel genes by comparing exomes from patients with similar features. | 1 | Biochemistry |
Armodafinil exhibits linear time-independent kinetics following single and multiple oral dose administration. Increase in systemic exposure is proportional over the dose range of 50–400 mg. No time-dependent change in kinetics was observed through 12 weeks of dosing. Apparent steady state for armodafinil was reached within 7 days of dosing. At steady state, the systemic exposure for armodafinil is 1.8 times the exposure observed after a single dose. The concentration-time profiles of the (R)-(−)-enantiomer following a single dose of 50 mg Nuvigil or 100 mg Provigil (modafinil being a 1:1 mixture of (R)-(−)- and (S)-(−)- enantiomers) are nearly superimposable. However, the C of armodafinil at steady state was 37% higher following administration of 200 mg Nuvigil than the corresponding value of modafinil following administration of 200 mg Provigil due to the more rapid clearance of the (S)-(+)-enantiomer. | 4 | Stereochemistry |
With the advent of asymmetric catalysis, it is necessary to consider the practicality of utilizing kinetic resolution for the preparation of enantiopure products. Even for a product which can be attained through an asymmetric catalytic or auxiliary-based route, the racemate may be significantly less expensive than the enantiopure material, resulting in heightened cost-effectiveness even with the inherent "loss" of 50% of the material. The following have been proposed as necessary conditions for a practical kinetic resolution:
* inexpensive racemate and catalyst
* no appropriate enantioselective, chiral pool, or classical resolution route is possible
* resolution proceeds selectively at low catalyst loadings
* separation of starting material and product is facile
To date, a number of catalysts for kinetic resolution have been developed that satisfy most, if not all of the above criteria, making them highly practical for use in organic synthesis. The following sections will discuss a number of key examples. | 4 | Stereochemistry |
Quantitation by indirect calorimetry, as opposed to the Harris-Benedict equation, is needed to accurately measure REE in cancer patients. | 1 | Biochemistry |
The Littrow expansion/compression effect is an anamorphic distortion of single-wavelength image on the focal plane of the instrument, due to a geometric effect surrounding reflection or transmission at the grating. In particular, the angle of incidence and reflection from a flat mirror, measured from the direction normal to the mirror, have the relation
which implies
so that an image encoded in the angle of collimated light is reversed but not distorted by the reflection.
In a spectrograph, the angle of reflection in the dispersed direction depends in a more complicated way on the angle of incidence:
where is an integer and represents spectral order, is the wavelength of interest, and is the line spacing of the grating. Because the sine function (and its inverse) are nonlinear, this in general means that
for most values of and , yielding anamorphic distortion of the spectral image at each wavelength. When the magnitude is larger, images are expanded in the spectral direction; when the magnitude is smaller, they are compressed.
For the special case where
the reflected ray exits the grating exactly back along the incident ray, and ; this is the Littrow configuration, and the specific angle for which this configuration holds is the Littrow angle. This configuration preserves the image aspect ratio in the reflected beam. All other incidence angles yield either Littrow expansion or Littrow compression of the collimated image. | 7 | Physical Chemistry |
Anadara trapezia, the Sydney cockle (NSW), or ark cockle (Queensland), is an estuarine filter-feeding bivalve. Its calcareous, heavily ribbed shell can grow to approximately across. Its range is along the east coast of Australia, from Queensland to Victoria. It has previously existed in Western Australia, South Australia, and the coast of New Zealand during the Middle Holocene. It has been used as a bioindicator/indicator species to study levels of the metals selenium, copper and cadmium. | 2 | Environmental Chemistry |
In June 2002, West Australian resident Rob Hall was convicted for using a canister of pepper spray to break up an altercation between two guests at his home in Midland. He was sentenced to a good behavior bond and granted a spent conviction order, which he appealed to the Supreme Court. Justice Christine Wheeler ruled in his favor, thereby legalizing pepper spray in the state on a case-by-case basis for those who are able to show a reasonable excuse.
On 14 March 2012, a person dressed entirely in black entered the public gallery of the New South Wales Legislative Council and launched a paper plane into the air in the form of a petition to Police Minister Mike Gallacher calling on the government to allow civilians to carry capsicum spray. | 1 | Biochemistry |
The partition coefficient between n-Octanol and water is known as the n-octanol-water partition coefficient, or K. It is also frequently referred to by the symbol P, especially in the English literature. It is also known as n-octanol-water partition ratio.
K, being a type of partition coefficient, serves as a measure of the relationship between lipophilicity (fat solubility) and hydrophilicity (water solubility) of a substance. The value is greater than one if a substance is more soluble in fat-like solvents such as n-octanol, and less than one if it is more soluble in water. | 7 | Physical Chemistry |
Several other methods for the electrophilic formation of C-N bonds are available. Nitrites and nitrates can be used to form oximes and nitro compounds, respectively. Additionally, organoboranes can serve the role of the nucleophile and often provide higher yields with fewer complications than analogous carbanions. The Neber rearrangement offers an alternative to electrophilic amination through the intermediacy of an azirine. | 0 | Organic Chemistry |
LC–MS is used in proteomics as a method to detect and identify the components of a complex mixture. The bottom-up proteomics LC–MS approach generally involves protease digestion and denaturation using trypsin as a protease, urea to denature the tertiary structure, and iodoacetamide to modify the cysteine residues. After digestion, LC–MS is used for peptide mass fingerprinting, or LC–MS/MS (tandem MS) is used to derive the sequences of individual peptides. LC–MS/MS is most commonly used for proteomic analysis of complex samples where peptide masses may overlap even with a high-resolution mass spectrometry. Samples of complex biological (e.g., human serum) may be analyzed in modern LC–MS/MS systems, which can identify over 1000 proteins. However, this high level of protein identification is possible only after separating the sample by means of SDS-PAGE gel or HPLC-SCX. Recently, LC–MS/MS has been applied to search peptide biomarkers. Examples are the recent discovery and validation of peptide biomarkers for four major bacterial respiratory tract pathogens (Staphylococcus aureus, Moraxella catarrhalis; Haemophilus influenzae and Streptococcus pneumoniae) and the SARS-CoV-2 virus.
LC–MS has emerged as one of the most commonly used techniques in global metabolite profiling of biological tissue (e.g., blood plasma, serum, urine). LC–MS is also used for the analysis of natural products and the profiling of secondary metabolites in plants. In this regard, MS-based systems are useful to acquire more detailed information about the wide spectrum of compounds from a complex biological samples. LC–nuclear magnetic resonance (NMR) is also used in plant metabolomics, but this technique can only detect and quantify the most abundant metabolites. LC–MS has been useful to advance the field of plant metabolomics, which aims to study the plant system at molecular level providing a non-biased characterization of the plant metabolome in response to its environment. The first application of LC–MS in plant metabolomics was the detection of a wide range of highly polar metabolites, oligosaccharides, amino acids, amino sugars, and sugar nucleotides from Cucurbita maxima phloem tissues. Another example of LC–MS in plant metabolomics is the efficient separation and identification of glucose, sucrose, raffinose, stachyose, and verbascose from leaf extracts of Arabidopsis thaliana. | 3 | Analytical Chemistry |
In physical chemistry, the Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van t Hoff who had noted in 1884 that the van t Hoff equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and reverse reactions. This equation has a vast and important application in determining the rate of chemical reactions and for calculation of energy of activation. Arrhenius provided a physical justification and interpretation for the formula. Currently, it is best seen as an empirical relationship. It can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, and many other thermally induced processes and reactions. The Eyring equation, developed in 1935, also expresses the relationship between rate and energy. | 7 | Physical Chemistry |
The persistent radical effect (PRE) in chemistry describes and explains the selective product formation found in certain free-radical cross-reactions. In these type of reactions, different radicals compete in secondary reactions. The so-called persistent (long-lived) radicals do not self-terminate and only react in cross-couplings. In this way, the cross-coupling products in the product distribution are more prominent.
The effect was first described in 1936 by Bachmann & Wiselogle. They heated pentaphenylethane and observed that the main reaction product was the starting product (87%) with only 2% of tetraphenylethane formed. They concluded that the dissociation of pentaphenylethane into triphenylmethyl and diphenylmethyl radicals was reversible and that persistent triphenylmethyl did not self terminate and transient diphenylmethyl did to a certain extent. In 1964, Perkins performed a similar reaction with phenylazotriphenylmethane in benzene. Again, the dimerization product of the persistent radical (phenylcyclohexydienyl) was absent as reaction product. In 1981, Geiger and Huber found that the photolysis of dimethylnitrosamine into dimethylaminyl radical and nitrous oxide was also completely reversible. A similar effect was observed by Kräutler in 1984 for methylcobalamin. The term persistent radical effect was coined in 1992 by Daikh and Finke in their work related to the thermolysis of a cyanocobalamin model compound.
The PRE is a kinetic feature which provides a self-regulating effect in certain controlled/living radical polymerization systems such as atom transfer radical polymerization and nitroxide mediated polymerization. Propagating radicals P* are rapidly trapped in the deactivation process (with a rate constant of deactivation, k) by species X, which is typically a stable radical such as a nitroxide. The dormant species are activated (with a rate constant k) either spontaneously/thermally, in the presence of light, or with an appropriate catalyst (as in ATRP) to reform the growing centers. Radicals can propagate (k) but also terminate (k). However, persistent radicals (X), as stated above, cannot terminate with each other but only (reversibly) cross-couple with the growing species (k). Thus, every act of radical–radical termination is accompanied by the irreversible accumulation of X. Consequently, the concentration of radicals as well as the probability of termination decreases with time. The growing radicals (established through the activation–deactivation process) then predominantly react with X rather than with themselves. | 0 | Organic Chemistry |
The PFT can be released in a variety of ways, depending on the application, and may be as simple as spraying into the air. Samples are then collected at set times and locations, and either taken to a laboratory for analysis, or analysed in the field.
Analysis of the samples typically involves three parts; preparation, chromatography and detection. Preparation involves removal of other impuries, for example, mixing with hydrogen then passing over a catalyst to convert oxygen to water, which is then removed with silica gel. The sample is then admitted to a gas chromatograph. This splits up the different PFTs, so a concentration value can be determined for each one.
There are two ways PFTs are then detected; using an electron capture detector or negative ion mass spectrometry. Both techniques involve bombarding the sample with electrons, and measuring the negative ions produced. Perfluorocarbons have a particularly high affinity for electrons, so are detected in low concentrations.
An alternative set up; the chromatograph can be omitted, and the different PFTs determined from their different masses in the mass spectrum.
PFTs can be detected in concentrations as low a 1 part in 10 by volume (1 femtolitre in a litre). | 2 | Environmental Chemistry |
The atmosphere is 21% oxygen by volume, which equates to a total of roughly 34 × 10 mol of oxygen. Other oxygen-containing molecules in the atmosphere include ozone (O), carbon dioxide (CO), water vapor (HO), and sulphur and nitrogen oxides (SO, NO, NO, etc.). | 5 | Photochemistry |
SCS facilitates the flux of molecules into other metabolic pathways by controlling the interconversion between succinyl CoA and succinate. This is important because succinyl CoA is an intermediate necessary for porphyrin, heme, and ketone body biosynthesis. | 1 | Biochemistry |
The aquatic inorganic carbon system is composed of the various ionic, dissolved, solid, and/or gaseous forms of carbon dioxide in water. These species include dissolved carbon dioxide, carbonic acid, bicarbonate anion, carbonate anion, calcium carbonate, magnesium carbonate, and others. The relative amounts of each species in a body of water depends on physical variables including temperature and salinity, as well as chemical variables like pH and gas partial pressure. Variables like alkalinity and dissolved (or total) inorganic carbon further define a mass and charge balance that constrains the total state of the system.
Given any two of the four central inorganic carbon system parameters (pH, alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide) the remainder may be derived by solving a system of equations that adhere to the principles of chemical thermodynamics.
For most of the 20th century, chemical equilibria in marine and freshwater systems was calculated according to various conventions, which led to discrepancies among laboratories' calculations and limited scientific reproducibility. Since 1998, a family of software programs called CO2SYS has been widely used. This software calculate chemical equilibria for aquatic inorganic carbon species and parameters. Their core function is to use any two of the four central inorganic carbon system parameters (pH, alkalinity, dissolved inorganic carbon, and partial pressure of carbon dioxide) to calculate various chemical properties of the system. The programs are widely used by oceanographers and limnologists to understand and predict chemical equilibria in natural waters. | 9 | Geochemistry |
Thermal desorption is an environmental remediation technology that utilizes heat to increase the volatility of contaminants such that they can be removed (separated) from the solid matrix (typically soil, sludge or filter cake). The volatilized contaminants are then either collected or thermally destroyed. A thermal desorption system therefore has two major components; the desorber itself and the offgas treatment system.
Thermal desorption is not incineration. | 2 | Environmental Chemistry |
The use of Fmoc as a temporary protecting group for amine at the N-terminus in SPPS is very widespread for Fmoc/tBu approach, because its removal with piperidine solution does not disturb the acid-labile linker between the peptide and the resin. A typical SPPS Fmoc deprotection is performed with a solution of 20% piperidine in N,N-dimethylformamide (DMF).
Common deprotection cocktails for Fmoc during SPPS:
* 20% piperidine in DMF (Fmoc group has an approximate half life of 6 seconds in this solution)
* 5% piperazine, 1% DBU and 1% formic acid in DMF. This method avoids the use of strictly controlled piperidine. No side product was observed for a peptide with 9 residues synthesized with this method. | 1 | Biochemistry |
Many living organisms employ toxins offensively or defensively. A relatively small number of toxins are known to have the potential to cause widespread sickness or casualties. They are often inexpensive and easily available, and in some cases it is possible to refine them outside the laboratory. As biotoxins act quickly, and are highly toxic even at low doses, they can be more efficient than chemical agents.
Due to these factors, it is vital to raise awareness of the clinical symptoms of biotoxin poisoning, and to develop effective countermeasures including rapid investigation, response, and treatment. | 1 | Biochemistry |
The NASBA technique has been used to develop rapid diagnostic tests for several pathogenic viruses with single-stranded RNA genomes, e.g. influenza A, zika virus, foot-and-mouth disease virus, severe acute respiratory syndrome (SARS)-associated coronavirus, human bocavirus (HBoV) and also parasites like Trypanosoma brucei.
Recently, NASBA reaction with fluoresce, dipstick and next generation sequencing readout has been developed for COVID-19 diagnosis. | 1 | Biochemistry |
Gallic acid is formed from 3-dehydroshikimate by the action of the enzyme shikimate dehydrogenase to produce 3,5-didehydroshikimate. This latter compound spontaneously rearranges to gallic acid. | 1 | Biochemistry |
PLCB1; PLCB2; PLCB3; PLCB4; PLCD1; PLCD3; PLCD4; PLCE1;
PLCG1; PLCG2; PLCH1; PLCH2; PLCL1; PLCL2; PLCZ1 | 1 | Biochemistry |
In histology and microscopy, Congo red is used for staining in amyloidosis, and for the cell walls of plants and fungi, and for the outer membrane of Gram-negative bacteria. Apple-green birefringence of Congo red stained preparations under polarized light is indicative of the presence of amyloid fibrils. Additionally, Congo red is used for the diagnostics of the Shigella flexneri serotype 2a, where the dye binds the bacterium's unique lipopolysaccharide structure.
Furthermore, Congo red may also be used to induce expression of the type III secretion system of Shigella flexneri, bringing about the secretion of IpaB and IpaC, which form translocation pores within host cell membrane, allowing effector proteins to pass through and alter the host cells biochemistry. The dye can also be used in flow cytometry experiments for the detection of Acanthamoeba, Naegleria' and other amoebal cysts.
In confocal microscopy, Congo red can be used as a stable fluorescent stain. | 3 | Analytical Chemistry |
The orientation of crystallites can be random with no preferred direction, called random texture, or directed, possibly due to growth and processing conditions. While the structure of a single crystal is highly ordered and its lattice is continuous and unbroken, amorphous materials, such as glass and many polymers, are non-crystalline and do not display any structures, as their constituents are not arranged in an ordered manner. Polycrystalline structures and paracrystalline phases are in between these two extremes. Polycrystalline materials, or polycrystals, are solids that are composed of many crystallites of varying size and orientation. Most materials are polycrystalline, made of a large number crystallites held together by thin layers of amorphous solid. Most inorganic solids are polycrystalline, including all common metals, many ceramics, rocks, and ice.
The areas where crystallites meet are known as grain boundaries. | 8 | Metallurgy |
The role of PA in the cell can be divided into three categories:
* PA is the precursor for the biosynthesis of many other lipids.
* The physical properties of PA influence membrane curvature.
* PA acts as a signaling lipid, recruiting cytosolic proteins to appropriate membranes (e.g., sphingosine kinase 1).
* PA plays very important role in phototransduction in Drosophila.
* PA is a lipid ligand that gates ion channels. See also lipid-gated ion channels.
The first three roles are not mutually exclusive. For example, PA may be involved in vesicle formation by promoting membrane curvature and by recruiting the proteins to carry out the much more energetically unfavourable task of neck formation and pinching. | 1 | Biochemistry |
A solar cells quantum efficiency value indicates the amount of current that the cell will produce when irradiated by photons of a particular wavelength. If the cells quantum efficiency is integrated over the whole solar electromagnetic spectrum, one can evaluate the amount of current that the cell will produce when exposed to sunlight. The ratio between this energy-production value and the highest possible energy-production value for the cell (i.e., if the QE were 100% over the whole spectrum) gives the cell's overall energy conversion efficiency value. Note that in the event of multiple exciton generation (MEG), quantum efficiencies of greater than 100% may be achieved since the incident photons have more than twice the band gap energy and can create two or more electron-hole pairs per incident photon. | 7 | Physical Chemistry |
If the concentration at the time t = 0 is different from above, the simplifications above are invalid, and a system of differential equations must be solved. However, this system can also be solved exactly to yield the following generalized expressions:
When the equilibrium constant is close to unity and the reaction rates very fast for instance in conformational analysis of molecules, other methods are required for the determination of rate constants for instance by complete lineshape analysis in NMR spectroscopy. | 7 | Physical Chemistry |
Oral levels in mice and rats are 3547–2545 mg/kg body weight (male and female) and 474–365 (male and female), respectively. | 4 | Stereochemistry |
Prior to founding the Center for Biomedical Mass Spectrometry at Boston University School of Medicine in 1994, Costello was a senior research scientist and the associate director of the National Institutes of Health Research Resource for Mass Spectrometry at Massachusetts Institute of Technology for 20 years. She is a William Fairfield Warren Distinguished Professor and the director of the Center for Biomedical Mass Spectrometry at the Boston University School of Medicine.
Costello served as the president of the American Society for Mass Spectrometry (2002–2004), the Human Proteome Organization (2011–2012), and the International Mass Spectrometry Foundation (2014–2018). She currently serves on the board of directors of the US Human Proteome Organization, and the editorial board of Clinical Proteomics. | 1 | Biochemistry |
The location of the ropB gene is directly and sequentially proximal to the subject of its transcriptional regulation (speB) which lies downstream of a 941 bp intergenic region between the two. Transcription of the ropB gene seems to necessitate a promoter within a series sequences between 238 and 480 bp and up to 800 bp upstream of the gene itself inside the highly repetitive intergenic region. | 1 | Biochemistry |
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